This invention relates to lifting mechanisms and particularly to new and improved jack arrangements which increase stability during operation.
In the lifting of unbalanced loads with a jack, and particularly cars and trucks, the weight of the vehicle is not equally distributed about the jack saddle or lift point. During operation, the unequal weight distribution causes the vehicle to tilt as one wheel is raised and the other three remain on the ground. This tilting causes a shift in the lift point related to the vehicle's suspension design and the ratio of wheel base to track.
Current bumper jacks accommodate lift point shift by a loose fit between the column and pedestal. The loose fit allows the column to tilt as the jack is operated. The weight of the vehicle, however, is applied to the jack base at an off-perpendicular angle which may be resolved into horizontal and vertical components. If an impact or force is applied to the vehicle during lifting, an additional shift of the lift point occurs and tilt of the column is increased. The horizontal component of the weight supported by the jack then becomes sufficient to overcome the friction between the jack base and the ground. The base then slips horizontally and the vehicle falls from the jack.
This invention is designed to prevent jack failure during lifting. In addition to impacts applied to the wheel, failure may occur due to leaning on the side of the vehicle, slamming a door, or using a lug wrench to loosen or tighten a wheel. The probability of slippage will also be increased if the jack column is not initially positioned perpendicular to the base. In the invention, column tilt is prevented by a novel base design while a new and improved saddle assembly accommodates lift point shift. The saddle assembly absorbs and dissipates the effects of all but the most severe extraneous impacts.
The prior art includes U.S. Pat. No. 3,232,584 to J. C. Miles which shows a folding base member for a screw-type jack having straight pivotally mounted legs or support members that are carried by the base plate and which have connected to the upper legs thereof an anchor boss for supporting the vertical jack column. The base member and the leg members are different in configuration and operation from the arrangements set forth herein. Neither the leg members nor the base of the Miles patent permit the flexing within defined limits which is possible with the present invention. The patent also fails to disclose a saddle which compensates for the elements of lift point shift during normal operation and the problems arising from impacts or unusual forces which are unanticipated. A conventional flat screw head is the lifting element in the Miles patent.
U.S. Pat. No. 3,184,205 to L. J. Carpezzi discloses a base member having curved legs which support the lower portion of the jack column at their upper ends. The leg members of the patent, however, are mounted in a rigid manner to the base and the curve of the legs is opposite to the configuration proposed herein. The base as shown in Carpezzi is a flat wheeled member having a central aperture. The Carpezzi patent thus differs substantially from the present structure and completely fails to disclose a saddle of the type to which a claim of novelty is directed herein.
The prior art also includes U.S. Pat. No. 2,502,037 to J. Erikainen on a vehicle bumper jack, U.S. Pat. No. 2,960,308 to H. J. O'Donnell on a telescopic jack, and U.S. Pat. No. 3,493,209 to R. C. Brammer on a stabilizing jack base. These patents are quite different from the present invention and are merely cited to be of interest for the general disclosures contained therein.
In summary, other patents may, of course, exist and be pertinent, but the above represents a cross-section of the best prior art of which applicant is aware. None of the references disclose the unique combination of features proposed herein. It appears, therefore, that the invention is patentable.